Cut across middle of sponge cake forming two layers, each about 1 1/2 inches high. Blend coffee and rum/Kahlua. Sprinkle enough of mixture over bottom half of cake to flavor it strongly. Don’t moisten cake too much or it may collapse on serving.
Beat room-temperature cheese and 1 cup sugar until sugar is completely dissolved and cheese is light and spreadable. Test for sweetness during beating, adding more sugar if needed.
Spread cut surface of bottom layer with half of the cheese mixture. Replace second layer and top this with remaining cheese mixture. Top with Cool Whip. Sprinkle top liberally with sifted cocoa and chocolate shavings.
Refrigerate cake for at least 2 hours before cutting and serving.